Method for removing deposits from interior surfaces of regenerative heat exchangers

ABSTRACT

A method for removing deposits from interior passageways of regenerative heat exchangers, particularly from the checker surfaces of regenerators for coke ovens, while maintaining the equipment in service by introducing a reactive material into the gas stream entering the heat exchanger. The reaction products of the deposit and reactive material are friable or volatile at operating temperatures and are passed into the stack gases. A preferred reactive material is anhydrous hydrochloric acid.

United States Patent Rounds June 10, 1975 [54] METHOD FOR REMOVING DEPOSITS 2,619,434 11/1952 Kraus et 134/2 2,900,285 8/1959 Darmann et a1. 134/19 X gggggg gvggggggg gg X 3,472,907 10/1969 Coberly 165/5 X [75] Inventor: Gerald L. Rounds, Fontana, Calif.

[73] Assignee: Kaiser Steel Corporation, Fontana, Primary E-Xami"e"A|ben Davis C lif Attorney, Agent, or Firm-Fulwider, Patton, Rieber,

L & Ut ht 22 Filed: on. 1, 1973 cc A method for removing deposits from interior pas- [52] U.S. C1. 165/1; 165/5; 134/2; Sageways of regenerative hcat exchangers, particularly 134/19* 134/31 201/2 202/241 423/107 from the checker surfaces of regenerators for coke ov- [51] Int. Cl. F28g 13/00 ens while maintaining the equipment in service by 1581 held of Search 165/5 95; 201/21 t'roducing a reactive material into the gas stream en- 202/14l 144' 241; 423/107' 134/2 tering the heat exchanger. The reaction products of 3 the deposit and reactive material are friable or volatile at operating temperatures and are passed into the [56] References cued stack gases. A preferred reactive material is anhydrous UNITED STATES PATENTS hydrochloric acid 1,097,196 5/1914 Sperr, Jr. 202/241 1,628,952 511927 Cregan 423/108 10 Claims 1 Drawing F131!" g! 1 3 e I I 1 1 1 -2 1 i I I 1 i, a 1 L 1 I i 1 1 1 1 I 1 I I I 1 1 I I I I l I I I I 1 I I 1 I 1 l 1 7 1 a 15 4 F 1 4 p 63 .53 j if Fuzz 4/2 n15: 4/1

METHOD FOR REMOVING DEPOSITS FROM INTERIOR SURFACES OF REGENERATIVE HEAT EXCHANGERS BACKGROUND OF THE INVENTION This invention relates to the removal of deposits from the interior passages of furnace regenerators and the like.

In destructive distillation, the production of steam and other manufacturing and processing techniques requiring the use of heat, it is normal practice to preheat the air and, at times, the fuel in order to increase the efficiency to combustion and reduce the amount of fuel utilized in the heating process. Preheating is conducted in regenerative heat exchangers referred to as regenerators. These regenerators normally consist of heat exchanging materials such as for example silicate bricks, which are also referred to as checkers. The checkers or interior of the regenerator are provided with a miltiplicity of passages for the dispersal and passage of the fuel, air or combustion gases through the regenerator while contacting as large a surface area of the heat exchange material as is possible. In operation the regenerators are heated by passing the combustion gases from the furnace for heating operation through the regenerator passages, thus transferring the heat from the combustion gases to the heat exchanging material. After reaching the desired temperature, the flow cycle is reversed and the air and fuel, if it is being preheated, are passed through the hot regenerators thereby transfer ring the heat in the heat exchange material to the air or fuel. In practice, regenerators are normally operated in sets or banks so that while one set or bank is being heated another set or bank is utilized for preheating.

In any heating operation the cost of fuel is a major item in the cost of the operation. Likewise, availability of fuel has become an important consideration during the last few years. It is generally true that lower grade fuels, that is fuels having a lower BTU content and high impurities are generally less expensive and more readily available than higher grade fuels. Thus, for example, in the case of the destructive distillation of coal to produce coke for steel making, it is highly desirable to utilize blast furnace gas as the fuel used in the manufacture of coke. Blast furnace gas is a by-product produced during the refining of the iron ore and is readily available in those areas where ore refining is conducted, particularly in an integrated mill where ore refining and other steel making operations are located at a single plant, or area. Likewise, blast furnace gas, as an ore refining by-product, must be disposed of in some manner. Blast furnace gas is a relatively low BTU fuel and is usually preheated in order to provide sufficient combustion efficiency for practical use in the production of coke. However, blast furnace gas contains certain impurities, particularly zinc, which over a period of time will form a build up of oxide deposits in the passages of the regenerators. These oxide deposits eventually reduce the size of the passages through the regenerators and increase the pressure drop through the regenerators to the extent that after a period of time it becomes impossible to pass enough of the blast furnace gas through the regenerators to provide sufficient combustion to maintain the temperature of the oven. Since, prior to this invention, no practical method for cleaning the regenerator passages of coke ovens and the like has been disclosed, the eventual result has been that it is necessary to switch to a more expensive higher BTU content fuel, such as natural gas or coke oven gas, while disposing of the blast furnace gas by burning or flaring without utilizing its heat content for useful purposes.

While the invention will be described hereinafter in connection with the utilization of blast furnace gas as a source of fuel for coke ovens, it should be understood that the principles thereof are applicable to other operations where deposits from fuel or other sources are formed in regenerator passages or other inaccessible areas, which deposits resist removal at the operating temperatures at which the equipment wherein the deposits occur is operated.

Accordingly, it is an object of this invention to provide a method for removing deposits from regenerative heat exchanger interior surfaces without the necessity of taking the equipment out of service and with substantially no damage to the equipment.

Another object of this invention is to provide a method for cleaning furnace regenerators and the like of deposits fonned by impure fuel whereby the use of impure fuel can be tolerated thus effecting a substantial economy in operation and conserving higher quality fuels such as natural gas and oil.

These and other objects and advantages of this invention will become apparent upon a reading of the detailed description of the invention and the claims appended thereto.

SUMMARY OF THE INVENTION The foregoing objects and advantages of this invention are accomplished by the introduction of a deposit reactive material into the regenerator passages while maintaining the regenerator in service and substantially at operating temperatures where it reacts with the deposit to form reaction products which are readily removed at the operating temperatures of the regenerator. Preferably the reaction products are volatile at operating temperatures and pass off with the stack gases. Any remaining non-volatile vestiges of the deposit are friable and readily flushed out of the regenerator passages by the flow of the gas passing therethrough.

In accordance with the method of this invention, the reactive material is added as a gas or finely divided liquid spray to the air, fuel or combination gases prior to the entrance thereof into the regenerator. The total amount of reactive material introduced into the regenerator during the course of treatment in accordance with the method of this invention is dependent upon the amount of deposited material to be reacted. The rate of introduction of reactive material is largely dependent upon the amount of time allowed for treatment, and the size of the equipment being treated. In the cleaning of coke oven regenerators good results are obtained when the oxide reactive material is introduced at a rate of about 2 C.F.M. (cubic feet per minute) per regenerator unit for a total treatment time of about 12 hours.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic diagram of a portion of a coke oven illustrating the flow of air and fuel through the regenerator system.

DESCRIPTION OF THE INVENTION The deposits which collect in regenerator passages are predominantly metal oxides, such as zinc oxide, aluminum oxide, sodium and potassium oxide, calcium and magnesium oxide although other materials such as carbon, metal sulfide and chlorides may also be present. The precise analysis of the deposit varies with the type of fuel being utilized and with the temperatures encountered in the regenerator system. In the case of deposits formed from blast furnace gas, the analysis shows that the major portion of the deposit thus formed consists of zinc oxide, which has a melting point about 1,800C. Thus, in the case of blast furnace gas the deposit comprises a matrix of zinc oxide, and includes other oxides such as silica, sodium oxide, and the like, which may not form deposits on their own under the conditions encountered in the regenerator, but which are bound by the zinc oxide matrix and contribute to the deposit formation.

The deposit reactive materials utilized in the method of this invention are characterized as being nonharmful to the regenerator equipment and brick work and as reactive with the deposit to form reaction byproducts which are readily removed from the regenerator and which, preferably, substantially little harmful effect on the environment when discharged from the system.

The reaction products must be readily removed from the regenerator by the heat and flow conditions extant in the regenerator. Preferably the reaction products are volatile at operating temperatures and are removed in the gas stream and discharged from the systems stack. Any remaining non-volatile vestiges of the reacted deposit are flushed out by the flow of gas.

The regenerators, particularly those exposed to high temperatures. are normally fabricated from ceramic brick or checkers and may include auxiliary equipment such as mild steel gates, valves and the like for controlling the flow of gaseous materials through the regenerator. It has been found that with the exception of hydrofluoric acid, materials that meet the other characteristics of a deposit reactive material in accordance with this invention have substantially no effect on the component parts of the regenerator when utilized in the manner of this invention.

In choosing the deposit reactive material for deposit removal in accordance with this invention, care must be taken that it does not decompose to form a poisonous gas or other deleterious substance. Thus, for example, cyanic acid and cyanogen halides would not be suitable for use in the method of this invention since they are highly poisonous.

Deposit reactive materials that meet the foregoing requirements include materials such as hydrochloric acid, sulfuric acid, carbon monoxide and hydorgen sultide. In addition hydrogen and chlorine in combination are useful deposit reactive materials.

Anhydrous hydrochloric acid is a highly preferred oxide reactive material for removing blast furnace gas deposits from regenerator passages. It is highly reactive with zinc oxide to form zinc chloride and water, both of which are vaporized at the flue temperatures of around l,lC. Likewise, carbon monoxide is also a highly preferred oxide reactive material since it forms volatile metal carbonyls with the metal cations of the oxide deposit.

The accompanying FIGURE is illustrative of a method of carrying out this invention as described in the following example.

Typical coke manufacturing apparatus is shown schematically in the FIGURE where a series of coke ovens 204, 205, 206 and 207 are provided for the destructive distillation of the coal. Each coke oven comprises an elongate substantially airtight chamber, the walls of which are constructed of heat exchange material, such as, for example, ceramic brick. Means, not shown. are provided for collecting the products of the destructive distillation of the coal and leading them out of the coke ovens as well as for charging coal to each of coke ovens 204, 205, 206 and 207. Combustion zones 104, 105, 106 and 107 are provided between coke ovens 204, 205, 206 and 207 respectively. The combustion zones 104, 105, 106 and 107 are in communication with each other through upper space 111 formed between the tops of the said coke ovens 204, 205, 206 and 207 and top wall 112. Igniting means 4, 5, 6 and 7 are provided in combustion chambers 104, 105, 106 and 107 respectively for combustion of the air fuel mixture. Below the coke ovens are air regenerators S1, 52, 53 and 54 and gas regenerators 61, 62, 63 and 64. As shown in illustration, the regenerators are arranged in pairs, that is, air regenerator 51 and gas regenerator 61 being paired and air regenerator 52 and gas regenerator 62 being paired and likewise for regenerator pairs 53 and 63 and 54 and 64. Each of the regenerators are constructed in a conventional manner, the interiors consisting of ceramic brick or checkers and being provided with a plurality of interior passages. The regenerators are designed to act as heat exchangers, either giving up heat to the air and fuel prior to combustion, or absorbing heat from the combustion gases after combustion.

in a typical operation cycle air is passed into heated regenerators, which are operated at a temperature of between 700 and l,l0OC, 51 and 53 for prewarming prior to combustion and fuel is let into heated regenerators 61 and 63 for preheating prior to combustion. The air and gas are mixed after leaving regenerators and ignited in combustion zones 104 and 106 by ignit ing means 4 and 6 respectively. The hot gti'aCS of combustion rise up through combustion zones 104 and 106, as shown by the broken lines, heating the sidewalls of the ovens 204, 205, 206 and 207, respectively. Passing through upper space 111 the gases from combustion chamber 104 pass downwardly through combustion chamber 105 and the gases from combustion chamber 106 pass downwardly through combustion chamber 107. Combustion gases, which have retained a substantial amount of heat, pass from chamber 105 and are directed into regenerators 52 and 62 for removing the heat from the combustion gas and heating the regenerator heat exchange material. Likewise, the hot combustion gases from chamber 107 are led into regenerators 54 and 64.

After approximately 20 minutes of operation in the manner described above, the preheating regenerators have begun to cool below the preferred operating temperatures and the regenerators being heated come up to operating temperatures. At this point, the flow of gas is shifted so that combustion now occurs in combustion chambers 105 and 107 with the air and fuel being preheated in regenerators 52 and 62 and 54 and 64 respectively. The combustion gases from chamber 104 are now led into regenerators 51 and 61 to reheat them and likewise with the combustion gases from chamber 106 which are led into regenerators 53 and 63.

It should be clear that the above description and illustration are schematic and an actual operation would involve many more regenerators and coke ovens and more complicated systems.

rate of about 2 C.F.M. into each of the regenerators being used to preheat the fuel. In the typical illustration and method for operating the coke oven set forth above, the anhydrous hydrochloric acid was initially The process of manufacturing coke by destructive 5 metered iI'ltO regenerators 61 and 63. Al the end of 20 distillation is well known in the art and does not form nutes the ycle was reversed and the acid was a part of this invention. switched to regenerators 62 and 64. The anhydrous hydrochloric acid was introduced into the regenerators at EXAMPLE both the pusher end and coke end of the furnace. The

A t i l k oven as ill str t d d d ib d 10 treatment was continued for a total period of 12 hours. above was selected for the testing of the method of this Following the treatment. th e O en as switched invention, because the regenerators were clogged to to blast furnace gas and operating temperatures were the point where the operating temperature of between maintained using blast furnace gas as a sole source of about 900 and about l,000C could not be maintained fuel indicating that the regenerators had been cleaned using blast furnace gas as fuel. The reason that the teml5 sufficiently to allow the use of blast furnace gas as the perature could not be maintained was due to the fact fuel for combustion. that the back pressure through the gas regenerators 61, While the foregoing example illustrates the use of the 62, 63 and 64 was so high that an insufficient amount method for removing deposits from the regenerators of of blast furnace gas was available in the combustion acoke oven, it should be clear that any regenerator, rechamber for proper maintenance of temperature. Recooperator or checker work can be cleaned using the generators 51, 52, 53 and 54 were restricted with commethod of this invention. Likewise, while the addition bustion gas deposits to such an extent that insufficient of oxide reactive material took place at the regeneraair could be passed through for proper combustion. tors used for preheating the fuel, it should be clear that Prior to the treatment of the regenerators of the coke it is preferred to add the oxide reactive material also to oven, samples of blast furnace gas from two blast furthe regenerators used for prewarming air since oxide naces, identified as blast furnace No. l and blast furdeposits also form in these regenerators from the comnace No. 3, were taken for analysis. The gas flow from bustion gases used to heat them. blast furnace No. l was 95,625 standard cubic feet per Also, as an alternative, the oxide reactive material minute (SCFM) and contained 0.018 grains per stancan be introduced in the upper portion of the combusdard cubic feet(Gr/SCF) ofparticulate matter. The gas tion zone which is designed as 111 in the FIGURE. flow from blast furnace No. 3 was measured at 96,580 Treatment time can be reduced by adding the oxide re- SCFM and contained 0.0380 Gr/SCF. The particulate active material both to the regenerators as described in matter from each of the samples was subjected to specthe example and in the upper space 111. in thi manner trometric analysis and the results are set forth in Table fresh oxide reactive material is introduced simulta- A below. neously to the regenerators used for preheating and to Table A Sample Zn Si Al CaO MgO Ni Sn,Cu,Pb

alas!l Furnace l7.5 6.4 3.0 4.4 2.5 Present Trace Blast Furnace 29.0 l0.3 4.4 5.8 3.1 Present Trace No. 3

The above analysis confirmed the presence of a the regenerators being heated. rather significant amount of zinc. While the foregoing constitutes a description of the An analysis of the deposits taken from the regenerapreferred embodiment of this invention, it should be tor brick prior to treatment showed that the deposit understood that numerous changes and modifications contained substantial amounts of zinc oxide ranging are possible without departing from the scope of the infrom about 30 to about 70 weight percent of the devention, as will be claimed hereinafter. posit. The second largest component was silicon diox- I claim: ide, which ranged from about 11 weight percent to about 35 weight percent. iron oxide and aluminum 1. In a regenerative heat exchanger having heat exoxide together Comprised about 20 to about 4() i h change surfaces on which deposits, including metal oxpercent of the deposit, while the oxides of titanium, caldes, ha e formed, a method for removing said deposits i magnesium, potassium d di d up th from said surfaces while maintaining said regenerative t f th d it, heat exchanger in operation comprising the steps of Anhydrous hydrochloric acid (gaseous) was selected maintaining said heat exchanger substantially at operas the oxide reactive material since from calculation of ating temperatures, causing a gas stream to flow in said free energy in the heats reaction with zinc oxide it was exchanger thereby to contact said heat exchange surdetermined that the reaction would proceed without faces, introducing a deposit reactive material into said the need for energy in the form of heat from the regengas stream thereby to carry said deposit reactive mateerator. Likewise, zinc chloride, one of the reaction rial into contact with said deposit for reaction with at products, is volatile at the combustion zone temperatures of 900 to l,l00C. The reaction products, zinc chloride and water, are not harmful to the environment and can be vented into the stack gases.

The anhydrous hydrochloric acid was metered at the least a major portion thereof to form reaction products, and removing said reaction products from said heat exchanger.

2. The method of claim 1 wherein said reaction products are volatile at said operating temperature of said heat exchanger and are carried out of said heat exchanger by said gas stream.

3. The method of claim 1 wherein said operating temperature ranges from between about 900 and l,lC.

4. The method of claim 1 wherein said deposit reactive material is introduced into said gas stream as a gas.

5. The method of claim 1 wherein said deposit reactive material is introduced into said gas stream as a liquid spray.

6. The method of claim 1 wherein said deposit reactive material is selected from the group consisting of hydrochloric acid, sulfuric acid, carbon monoxide, hydrogen, sulfide, hydrogen chlorine and combinations thereof.

hours.

* k t i 

1. IN A REGENERATIVE HEAT EXCHANGER HAVING HEAT EXCHANGE SURFACES ON WHICH DEPOSITS, INCLUDING METAL OXIDES, HAVE FORMED, A METHOD FOR REMOVING SAID DEPOSITS FROM SAID SURFACES WHILE MAINTAINING SAID REGENERATIVE HEAT EXCHANGER IN OPERATION COMPRISING THE STEPS OF MAINTAINING SAID HEAT EXCHANGER SUBSTANTIALLY AT OPERATING TEMPERATURES, CAUSING A GAS STREAM TO FLOW IN SAID EXCHANGER THEREBY TO CONTACT SAID HEAT EXCHANGER SURFACES, INTRODUCING A DEPOSIT REACTIVE MATERIAL INTO SAID GAS STREAM THEREBY TO CARRY SAID DEPOSIT REACTIVE MATERIAL INTO CONTACT WITH SAID DEPOSIT FOR REACTION WITH AT LEAST A MAJOR PORTION THEREOF TO FORM REACTION PRODUCTS, AND REMOVING SAID REACTION PRODUCTS FROM SAID HEAT EXCHANGER.
 2. The method of claim 1 wherein said reaction products are volatile at said operating temperature of said heat exchanger and are carried out of said heat exchanger by said gas stream.
 3. The method of claim 1 wherein said operating temperature ranges from between about 900* and 1,100*C.
 4. The method of claim 1 wherein said deposit reactive material is introduced into said gas stream as a gas.
 5. The method of claim 1 wherein said deposit reactive material is introduced into said gas stream as a liquid spray.
 6. The method of claim 1 wherein said deposit reactive material is selected from the group consisting of hydrochloric acid, sulfuric acid, carbon monoxide, hydrogen, sulfide, hydrogen chlorine and combinations thereof.
 7. The method of claim 1 wherein said deposit consists essentially of metal oxides and further comprises from about 30 to about 70 weight percent of zinc oxide.
 8. The method of claim 1 wherein said deposit reactive material is anhydrous hydrochloric acid in the gaseous form.
 9. The method of claim 8 wherein said anhydrous hydrochloric acid is introduced into said heat exchanger at the rate of 2 cubic feet per minute.
 10. The method of claim 9 wherein said deposit reactive material is introduced for a period of about 12 hours. 